This invention relates to the testing of pressurised containers, such as, but not solely, pharmaceutical pressurised metered dose inhalers (pMDI) and in particular to non invasive methods and apparatus for testing or measuring the internal vapour pressure of such containers.
Pressurised containers are used in a variety of fields, they may, for example provide a source of substance for dispensing. An example of such a container is used in the medical field where it may provide a supply of pharmaceutical substance for an inhaler, in particular a metered dose inhaler. It will be appreciated that there are a variety of other uses that such containers can be put to.
Containers for holding a suspension or solution of a pharmaceutical substance in a propellant under pressure are well known. One such known container comprises a body which defines a chamber, a valve stem which extends from a head of the body and a metering chamber which is selectively communicable by the valve stem with the atmosphere and the chamber; the valve stem providing, via an L-shaped conduit which extends between the free end and the side wall thereof, the outlet of the container through which metered doses of propellant containing pharmaceutical substance are delivered. The valve stem is axially displaceable between a first, extended position in which the metering chamber, and hence the container, is closed to the atmosphere since the L-shaped conduit is disposed wholly outside the metering chamber, and a second, depressed position, in which the metering chamber is in open communication with the outlet provided by the L-shaped conduit in the valve stem and through which a metered dose of propellant containing pharmaceutical substance is delivered. The container is filled with the valve stem in the depressed position, with the propellant containing pharmaceutical substance being forced downwardly through the L-shaped conduit in the valve stem, the metering chamber and into the chamber defined by the body of the container.
In the field of metered dose containers it is necessary to test or check the contents of such containers. Testing provides information on the level of pharmaceutical substance in the container and also the level of propellant. The level of pharmaceutical substance is important as it relates to the number of doses that the container can dispense. In some cases the level of pharmaceutical substance is set by regulation and the level in the container must fall within a narrow band.
One test performed on such containers is the measurement of the internal vapour pressure. This may be required for a number of reasons, for example, to ensure that air has been removed from the container in the purging stage of production, to ensure that the ratio of the blended propellants to the pharmaceutical substance is correct or to ensure that additional air has not been added to the container during production.
There are a variety of methods of filling such containers, which are known, for example European Patents having publication numbers EP1084059, EP1073587 and EP1080014,
However methods and apparatus for testing the internal vapour pressure of a metering container so filled have tended to be unrefined. Methods, which exist, consist of invasive techniques. For example, one known method involves piercing the base of an inverted container and connected the vapour in the headspace to a pressure gauge. After the measurement is complete the contents of the pMDI are vented to the atmosphere. However propellants generally used such as CFCs are considered harmful both to any operators which may be near by and to the general environment. In this method the full contents of the container must be vented and therefor wasted. As the test is destructive, lower yields result from performing the test during manufacture. One known technique of performing this method involves an operator simply piercing the container by means of a sharp object such as a spike. There are obviously other disadvantages of such a method such the risk of injury to the operator.
One further disadvantage of the method described above is that evaporation of the liquid propellant occurs when the device is vented thus leading to localised cooling of the apparatus, this affects the pressure reading of subsequent pMDIs.
There therefor exists a need for a method and apparatus for testing the internal pressure of a container by non invasive means.
Herein non invasive may be said to be defined as not involving the introduction of instruments or devices into the container being tested, in particular not involving the piercing of the container wall.
The present invention in at least one preferred aspect aims to provide an improved testing method or testing apparatus, which at least partially overcomes the above-mentioned problems.
The present invention also aims to provide a method and apparatus which are adapted to test or measure the internal pressure of a container reduces the amount of propellant alone or propellant containing pharmaceutical substance released to the atmosphere.
In a preferred form the present invention consists of apparatus for providing an indication of the level of contents of a pressurised metered dose container.
According to a first aspect of the present invention there is provided testing apparatus for testing a container containing a suspension or solution of a substance, in particular, but not solely, a pharmaceutical substance, in a propellant under pressure, said container comprising a body which defines a chamber, a valve stem which extends from a head of the body and a metering chamber which is selectively communicable by the valve stem with the atmosphere and the chamber; the valve stem providing; via an L-shaped conduit which extends between the free end and the side wall thereof, the outlet of the container through which metered doses of the substance are released from said container, said testing apparatus characterised in that it comprises: a gallery for communicating, in use, in a fluid-tight manner with said valve stem; actuating means, in use, actuating said valve stem so as to discharge a metered dose of substance into said gallery, repeatably, if necessary, until the pressure within the gallery is substantially equalised with the pressure within the container; pressure measuring means in communication, in use, with said gallery and providing a measurement of the pressure therein.
Preferably the actuating apparatus comprises a manually operated handle bearing against said valve stem.
Preferably the actuating means comprises a cam which in one position directly or indirectly actuates the valve stem.
Preferably the actuating means comprises electromechanicaly operable means which preferably automatically actuates the valve stem.
Preferably the pressuring measuring means comprises a pressure cell.
Preferably the pressure measuring means comprises means which provides a feedback into the manufacturing process of said containers providing adjustment of the process so that a pre-set limit of pressure within the containers is maintained.
According to another aspect of the present invention there is provided a method of testing a container containing a suspension or solution of a substance, in particular, but not solely, a pharmaceutical substance, in a propellant under pressure, said container comprising a body which defines a chamber, a valve stem which extends from a head of the body and a metering chamber which is selectively communicable by the valve stem with the atmosphere and the chamber; the valve stem providing, via an L-shaped conduit which extends between the free end and the side wall thereof, the outlet of the container through which metered doses of the substance are released from said container, said method characterised in that it comprises the steps of:
providing a gallery in fluid-tight communication with said valve stem;
actuating said valve stem so as to discharge a metered dose of substance into said gallery, repeatably, if necessary, until the pressure within the gallery is substantially equalised with the pressure within the container;
measuring the pressure within said gallery.
Preferably the actuating apparatus comprises a manually operated handle bearing against said valve stem.
Preferably the actuating means comprises a cam which in one position directly or indirectly actuates the valve stem.
Preferably the actuating means comprises electromechanicaly operable means which preferably automatically actuates the valve stem.
Preferably the pressuring measuring means comprises a pressure cell.
Preferably the pressure measuring means comprises means which provides a feedback into the manufacturing process of said containers providing adjustment of the process so that a pre-set limit of pressure within the containers is maintained.